1. Prior Art
Multi-stage transmissions of the type used for automobiles, trucks and the like may broadly be divided into two classes. In one class, which will be termed the parallel type, each stage is connectable between the input and output and only a single stage may be engaged at one time. Accordingly, when the transmission is shifted one stage must be disengaged and another stage engaged in synchronism. In the second class, which will be termed serial transmissions, the output of one stage is fed to the input of the next stage and each stage may be either engaged or disengaged so as to multiply its input power by either a first or second gear ratio. Typically, one of the gear ratios is unity.
In this serial class of transmissions, a shift simply involves the engagement of an additional higher stage or the disengagement of a previously engaged stage. In such transmissions, it is necessary to insure that when a particular stage is engaged, all lower stages are also engaged. This requirement is easily met employing shift levers which must be moved through definite sequences, so that, for example, the shift from neutral to third involves the sequential engagement of the first, second and then third stages. When a push button type electromechanical shift system is provided wherein the higher stage may be selected without previously engaging lower stages, means must be provided for insuring the proper set of engagements for each position of the actuator.